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Roger Weller, geology instructor

Dirt Houses
by Kevin Thompson
Physical Geology
Spring 2015


Dirt as an Alternate Construction Method in Housing


In 2014 the United States completed over 800,000 newly constructed houses. The majority of these houses where made from traditional materials. Wood, stick frame, with fiberglass insulation. Alternate housing techniques are few and far between. The simple economics of building a house makes the choices limited. Few housing contractors want to, or have the time to navigate the permits that would be required to build a house that varied from the normal market. The individual who chooses an alternative technique would have a unique house that also would have built-in benefits of insulation and aesthetics.

Resources available for construction and the transportation costs make the reality of buying a new home problematic for a growing number of Americans. Locally available materials and free materials found on site would enable an individual or family to construct a home. In the past the construction of a home was a family affair. This changed with the housing boom in the post-WW II years when suburbs where created and cheap transportation was available. Those realities have again shifted.    

There are dozens of housing options available. They range from straw bale to converting shipping containers. It is necessary to weigh the pros and cons of the options available when considering what type of construction is wanted. In the desert south west a traditional construction technique was Adobe bricks. Houses where made from adobe before Europeans settled this region. The pueblo culture used Adobe in Mesa Verde. The occupation of that settlement lasted until the 11th century. Adobe or similar techniques are used in arid regions around the world. Adobe provides thermal mass to hold heat in winter and to keep the dwelling cool in summer. Adobe and Cob are essentially the same material. Cob is unformed while Adobe is made into bricks. Cob is used throughout the world also.  

Adobe is simply mud bricks. However the type of mud and its consistency are paramount to a successful brick. Adobe is made of sand, clay and water. This mix can also contain organic material such as straw or manure added for strength. The quantities of the sand and clay vary.  The makeup of the mud used is necessary to ensure a strong brick. Modern Adobe is stabilized with Portland cement. This addition has an added advantage of making the Adobe resistant to water. Traditional Adobe houses used very little wood so the bricks would be “load Bearing” in other words the bricks would support the weight of the roof. Modern techniques could use post and beam to support the roof of the structure.

Several factors impact the traditional construction of bricks. Composition of the Adobe, temperature, and humidity effect the drying of the bricks. Cracking and breaking is an issue. Size of the bricks is relative to the drying time. Smaller bricks have fewer problems in high heat and low humidity, as they dehydrate at a more uniform speed; for larger bricks slower and cooler is required. Modern techniques in construction of bricks involve machinery and result in a uniform and consistent brick.

The technique for assembling the bricks into a wall is no different than laying fired bricks. Mortar is required between the layers and the wall is stacked. The exterior of the wall is sealed with several layers of stucco and the interior of the wall is plastered. This protects the bricks from the weather. The roof of the traditional dwelling is flat and made of wood beams and ocotillo with a layer of cob. However modern roofing allows for a better weather-proof cover and the eves help to keep water off the walls.

One of the simplest methods of construction is the Earth Bag. This second technique requires nothing more than sand bags and the ability to fill them. This technique uses bags filled with moist dirt that are stacked similarly to bricks. Some bags are several meters long. Between each layer barbed wire is laid to prevent movement of the bags. Once the desired form and height is reached a roof is constructed and the walls are also finished with stucco and plaster.

One of the advantages with earth bag construction is the wider range of architectural design possible. Domed ceilings and arches are simple to incorporate in the project. This method allows the builders to tailor the dwelling to their whim.

With a growing concern about the resources available and the economic realities of housing costs alternate building materials and techniques make sense. Both the Earth Bag and Adobe could be made with the owner/ builder labor that would reduce the cost of a newly constructed house by half per square foot of a traditional stick built house. The skills required to work these materials is significantly more forgiving than modern methods. Finally the thermal advantage of the materials makes the cost of living in these types of houses far less than a stick built house. 

Adobe bricks

Earth bag